The present invention relates to an airplane such as a civil or military airplane having turbojet engines, e.g. bypass engines, carried on a surface of the airplane such as the airplane fuselage or wing.
Present civil airplanes are propelled using turbojets that are fastened either under the wings by means of pylons, or on the fuselage, or indeed at the root of the tail fin, i.e. at the junction between the tail fin and the fuselage.
In the context of reducing fuel consumption, engine manufacturers are seeking to embed engines at least partially within a surface of the airplane so as to enable pylons to be eliminated together with their fairings, thus reducing the weight of the propulsion assembly and also the drag of the airplane. Furthermore, partially integrating engines in an airplane surface makes it possible to increase the diameter of the engines, thus making it possible to envisage using engines having a very large bypass ratio.
In flight, an air boundary layer forms on the surfaces of the airplane that are in contact with the surrounding air, thereby generating aerodynamic drag. The air boundary layer is due to air friction against the surfaces of the airplane. It has long been considered that engines ought not to ingest this boundary layer since that can impart large amounts of distortion to the fan and lead to vibration of the propulsion assembly, and airplanes have sometimes been fitted with boundary layer “traps” located upstream from the air inlets for engines that are partially embedded. That type of solution enhances the operability of turbojets and also their efficiency, but it is harmful to the propulsive efficiency of the assembly constituted by the airplane and its turbojets, thus increasing fuel consumption. The operability of a turbojet is defined as being its ability to operate in safe and reliable manner under a variety of operating conditions that include extreme conditions (e.g. ingesting a bird, compressor pumping, flow direction which consists in the air stream reversing in the compressor, . . . ).
Recent studies have shown that absorbing a portion of the boundary layer in engines serves to reduce the aerodynamic drag of the airplane and to reduce the speed of the air entering its engines, thereby increasing the efficiency of the engines.
In its patent application WO 2010/049610A1, the Applicant has proposed an airplane in which the turbojet nacelles are partially embedded in the fuselage. The air inlet of each engine is connected to the fuselage by walls for guiding the boundary layer, which walls extend upstream from the air inlet and splay apart from each other going upstream.
With such a configuration, a portion of the air from the boundary layer is guided to the air inlet of the engine, thereby enabling the aerodynamic drag of the airplane to be reduced and enabling the efficiency of the engine to be increased by lowering the speed of the air at the inlet of the turbojet.
Nevertheless, such ingestion of the boundary layer by the turbojet suffers from drawbacks in terms of turbojet operability. Ingesting boundary layer air at the inlet to a turbojet gives rise to major circumferential variation in the total pressure and in the speed of the air, since both the speed and the total pressure are smaller within the boundary layer.